My proposed research plan is directed at investigating how cells initiate and maintain filopodia. Filopodia are biologically significant in many contexts, such as presentation of antigen by dendritic cells, metastatsis of tumors, and neuronal pathfinding. Therefore, this study will foster general interest. The study will examine the regulatory molecule, fascin, and its role in the mechanism of filopodia formation. Preliminary data indicate that fascin is necessary and sufficient for bundling of actin filaments in filopodia. Furthermore, photobleaching experiments reveal rapid recovery of GFP-fascin in filopodia in vivo. Structural and kinetic analysis of fascin and actin in filopodia suggest that filopodial bundles are maintained by dynamic association of fascin with actin-filaments. However, the molecular mechanism describing fascin recruitment to filopodia remains elusive and, therefore, will be the subject of this proposal. The immediate goal of this research plan is to identify the molecular basis for filopodia formation and breakdown, namely, the recruitment of fascin and coordination of actin polymerization, bundling, and depolymerization. [unreadable] [unreadable] [unreadable]